Final answer:
Rule 5 of the COLREGs mandates that every vessel must always maintain a proper lookout using sight, hearing, and all other available means to ensure a full appraisal of the situation for safety.
Step-by-step explanation:
According to Rule 5 of the International Regulations for Preventing Collisions at Sea (COLREGs), every vessel must at all times maintain a proper lookout by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions to make a full appraisal of the situation and the risk of collision. This rule emphasizes the importance of vigilance on the water to ensure the safety of all vessels and their crews. The lookout must be able to detect other vessels, navigational hazards, and any relevant changes in the environment that could affect safe navigation.